Cytokines are soluble factors produced by lymphocytes that regulate the survival, proliferation, differentiation, and homeostasis of cells involved in mediating the immune response. These factors not only activate other lymphocytes, they also relay signals to non-lymphoid cells including macrophages, epithelial and stromal cells creating a broad spectrum of cytokine activity that is critical to the maintenance of health. Consequently, much effort has been devoted to the study of these proteins.
Interleukin-15, originally designated IL-T, is a member of the four-.alpha.-helix bundle cytokine family and mimics the biological activities of another cytokine, IL-2. These functional properties include the stimulation of LAK activity, GM-CSF and INF-gamma secretion by NK cells as well as the proliferation of T, B, and NK cells. This redundancy of function is due to the sharing of two of the three receptor subunits of the IL-2 receptor complex (Grabstein et al., Science, 1994, 264, 965-968). However, in bone marrow mast cells Interleukin-15 utilizes a novel receptor/signal transduction pathway which is independent of any of the IL-2 components (Tagaya et al., Embo J., 1996, 15, 4928-4939).
Interleukin-15 was initially isolated from two cell lines (HTLV-1-associated HuT-102 adult T cell leukemia and CV-1/EBNA) as a factor that stimulated T and B lymphocyte proliferation and NK cell activation yet it is not expressed by normal T cells (Bamford et al., Proc. Natl. Acad. Sci. U S A, 1996, 93, 2897-2902; Burton et al., Proc. Natl. Acad. Sci. U S A, 1994, 91, 4935-4939; Grabstein et al., Science, 1994, 264, 965-968).
The Interleukin-15 mRNA is, however, found in a variety of cell types including macrophages, B cells, thymic cells, activated vascular endothelial cells, bone marrow stromal cells, fibroblasts and activated monocytes. Furthermore, it is also found in the tissues of the placenta, skeletal muscle, kidney, lung, and heart (Tagaya et al., Immunity, 1996, 4, 329-336). Yet even with this wide intracellular distribution, only a few cell lines have been shown to secrete detectable amounts of active Interleukin-15 (Grabstein et al., Science, 1994, 264, 965-968). The limited secretion of the protein is thought to result from the fact that Interleukin-15 expression is negatively controlled at both the transcriptional and post-transcriptional level (Bamford et al., Proc. Natl. Acad. Sci. U S A, 1996, 93, 2897-2902).
Manifestations of altered Interleukin-15 regulation appear in a multitude of disease states. These include arthritis (McInnes and Liew, Immunol. Today, 1998, 19, 75-79), graft vs. host disease (Kumaki et al., Int. J. Hematol., 1998, 67, 307-312), multiple sclerosis (Kivisakk et al., Clin. Exp. Immunol., 1998, 111, 193-197), aberrant immune responses including HIV infections (Carson and Caligiuri, Braz. J. Med. Biol. Res., 1998, 31, 1-9), inflammation (Kirman et al., Inflamm. Res., 1998, 47, 285-289) and pulmonary sarcoidosis (Agostini et al., J. Immunol., 1996, 157, 910-918). However, the role of Interleukin-15 in the development of cancer has been the most broadly investigated.
Cellular transformation and acquisition of the metastatic phenotype are the two main changes normal cells undergo during the progression to cancer and several labs have linked these processes to the overexpression of Interleukin-15. Yamada et al. demonstrated that Interleukin-15 growth signals induce the development of adult T cell leukemia and the invasion and proliferation of ATL cells. This proliferative effect has also been demonstrated in granular lymphocytes of patients with lymphoproliferative diseases, and leukemic B cells from patients with chronic lymphocytic leukemia and hairy cell leukemia (Yamada et al., Blood, 1998, 91, 4265-4272). Interleukin-15 is also frequently expressed in human small cell lung cancers, often in two similar isoforms generated by alternative splicing (Meazza et al., Oncogene, 1996, 12, 2187-2192).
Currently, there are no known therapeutic agents which effectively inhibit the synthesis of Interleukin-15. To date, strategies aimed at inhibiting Interleukin-15 function have involved the use of monoclonal antibodies specific to Interleukin-15 and those targeting the shared subunits of the IL-2 receptor and mutant forms of the Interleukin-15 protein.
One monoclonal antibody to Interleukin-15, M110, has been used to inhibit the upregulation of natural killer (NK) and antibody-dependent cellular cytotoxicity (ADCC) activities in the peripheral blood mononuclear cells of HIV-sero-negative patients (Loubeau et al., J. Acquir. Immune Defic. Syndr. Hum. Retrovirol., 1997, 16, 137-145). Likewise, another commercially available antibody, Mill, was used to demonstrate that Interleukin-15 is involved in the regulation of markers of melanoma progression (Barzegar et al., Oncogene, 1998, 16, 2503-2512). Furthermore, humanized and bispecific-humanized antibodies to the IL-2 receptor .alpha. and .beta. subunits have been shown to reduce the Interleukin-15-induced proliferation of several cell types (Guex-Crosier et al., J. Immunol., 1997, 158, 452-458; Pilson et al., i J. Immunol., 1997, 159, 1543-1556). Finally, using site-directed mutagenesis, Kim et al. produced an InterLeukin-15 antagonist, a mutant Interleukin-15/murine Fcgamma2a fusion protein, which inhibited Interleukin-15-triggered cell proliferation in BAF-BO3 cells and blocked delayed-type sensitivity in mice (Kim et al., J. Immunol., 1998, 160, 5742-5748). However, these strategies are untested as therapeutic protocols as well as being non-specific because of the shared IL-2 receptor subunits.
Consequently, there remains a long felt need for additional agents capable of effectively and specifically inhibiting Interleukin-15 function. Antisense oligonucleotides are believed to provide a promising new pharmaceutical tool for the effective modulation or Interleukin-15 expression.